We saw what happened at daytona. In a split second the day at the races took a disastrous turn. Millions of americans attend professional sporting ts each year, so when are the most dangerous and do fans fully understand the risks involved? Abc's lindsay janice is on the case for us tonight. Oh, my god! Reporter: Shock and horror as fans realize what's just happened. This cellphone footage capturing their sheer disbelief. But this weekend's crash at the daytona track, isn't the first time racing fans have been hit with flying debris. There have been another accident. It involves one of our leaders today. Anda a wheel flying over the fencing. In 1998 at this indycar race in michigan, parts of a car hurdled into the stands, killing three fans. And the deadliest crash, this 1955 disaster at the le mans race in france. 83 spectators were killed. When a crash sent a car's engine and hood tearing through the crowd. In modern racing fans are rarely hurt. Injuries at sporting events, though usually minor are more common at baseball and hockey games. In 2002 after a flying puck struck and killed 13-year-old brittanie cecil, they increased safety netting to protect fans. What many don't realize, I they can't always sue if they're injured. Stadium owners and operators limit their liability through fine text on the ticket. It says, if you attend a sporting match, you waif your right to sue for any injury. This hockey ticket stub to new york's madison square garden reads, the holder assumes all risks and danger of personal injury and all other hazards in any way arising from the event. But some fans have fought back after getting hurt. Years ago susan rhodes was struck in the jaw from a broken bat. 12 surgeries later, she's suing the dodgers for her medical expenses. I see people sitting close with their children. I don't think they have any idea how dangerous is really is. Injuries are rare, but fans do take a risk when attending races and games. Experts tell us that increasing safety for the crowd would mean keeping them farther away from the action.

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